Storm Forecast
Valid: Sat 29 Mar 2008 06:00 to Sun 30 Mar 2008 06:00 UTC
Issued: Fri 28 Mar 2008 21:23
Forecaster: DAHL
SYNOPSIS
Atlantic zonal upper jet is slowly propagating eastwards towards Europe, with an imbedded trough reaching western Europe late in the period. Ahead of this feature, plume of warm/moist air is advected northeastwards into France. A weakening upper trough and an attendant weak SFC low pressure region circulation persist over the eastern Mediterranean.
DISCUSSION
... Iberian Peninsula ... France ...
It seems that weak CAPE will develop over the Iberian Peninsula late on Saturday, and slowly spread into France during the night in response to advectively steepening lapse rates and some low-level moistening. If these processes indeed suffice to result in positive CAPE, it will likely remain capped, given minimal upward motion. Consistent with that, model guidance does not suggest that appreciable precipitation will occur. Thinking is that an isolated thunderstorm or two may develop over Iberia in the late afternoon and evening hours, as well as over central France during the night.
Shear profiles over N Iberia and France will be quite supportive of severe evolution, including mesocyclones ... with strong LLS being beneficial for tornadogenesis. Also, marginally severe hail and severe wind gusts may occur, should persistent cells manage to form.
However, indications are that any storm will be quite isolated, and a categorical risk is not introduced at the moment. Situation should be monitored, however, and an upgrade may be issued on the course of Saturday if thunderstorm coverage turns out to be larger than currently anticipated. Model QPF does not suggest clear foci for convective evolution, suggesting a low predictability of the location of the convection. Thus, and owing to allover minimal signals, a thunderstorm area is not issued at this time.
... western Gulf of Biscay ...
Post-frontal cellular convection will spread across the western Bay of Biscay late in the period. This activity may be associated with sporadic lightning, which currently does not seem to warrant a separate thunderstorm forecast area.
... eastern Mediterranean ...
Scattered thunderstorms should persist in the vicinity of the SE Mediterranean upper low in weakly unstable and minimally capped air mass. Simulated shear, as well as thermodynamic profiles at low levels do not suggest that much of a severe convective threat exists with this activity.
